Conventionally, silver halide photographic materials, after exposure, are developed in a plurality of photographic processing baths. The processing of black and white photographic materials generally comprises a black and white development step, a fixing step and a washing step. The processing of colour photographic materials comprises a colour development step, a bleaching step, a fixing step and a washing step.
During the processing of these photographic materials, the composition of the processing bath changes. In particular, the photographic baths become loaded with chemical substances such as gelatin, latex, polymers, surfactant, and numerous other organic substances either initially incorporated into the photographic materials or released upon the reactions at the time of development. These substances contaminates the baths and reduces their efficacy. In addition, the presence of these contaminants in the photographic processing baths results not only in a variation in the sensitometry of the photographic materials but also a fouling of the processing machine and therefore of the materials which are processed therein. This phenomenon is all the more significant since photographic materials are generally processed in automatic processing machines. The machines which make it possible to develop photographic materials quickly are also fouled more quickly. In particular, there appear, in the photographic processing baths of these automatic machines, tars which originate from organic constituents of the photographic materials and which are deposited on the photographic material in the course of the processing and foul the machine. The presence of these tars requires a significant amount of maintenance of the processing machines, an earlier replacement of the baths and, in extreme cases, several successive steps of washing the photographic materials.
It is known from the art that this drawback can be remedied by adding surfactants to the baths during the processing with a view to dissolving the tars present. However, large amounts of these agents must be used and this modifies the stability and efficacy of the processing bath.
The accumulation, in the washing and/or stabilising baths, of substances resulting from the previous steps of the processing is not only prejudicial to the stability of the photographic images developed, to the obtention of unvarying sensitometric characteristics and to the maintenance of the equipment, but also interferes with the possibility of recycling these washing and stabilising baths or of discharging them to the drains. At the end of processing, compounds which contribute to raise the COD of the solution are found in the washing and stabilising baths.
The effluent can for example be subjected to electrolytic oxidation, dialysis, reverse osmosis (as described in the German patent application 3 246 897), flocculation, or oxidation with hydrogen peroxide, optionally coupled with UV treatment, as described in U.S. Pat. No. 5,439,599 of Gehin et al. It is also possible to combine non-catalytic oxidation with catalytic oxidation and biological treatment, as described in European patent application 690 025.
The treatments described in the literature usually recommend combining two or more techniques in order to obtain satisfactory decontamination of the effluent, enabling it to be discharged, or to eliminate the substances which would be prejudicial to re-use of the effluent. Some of these techniques also have a high cost of application. This is because it is desirable to develop a method which makes it possible to eliminate these substances and tars economically and rapidly, without impairing the sensitometric properties of the photographic materials processed and without modifying the stability or efficacy of the photographic processing baths.
The object of the present invention is to solve the afore mentioned problems associated with the presence of the organic substances and tars in the photographic processing baths.
Another object of the invention is to reduce the fouling of automatic processing machines and thus to make maintenance operations on these machines less frequent.